Arsenic sulfide glasses



April 6, 1965 'i'. c. -Macwov Filed April 22. 1960 3 Sheets-Sheet 1 INVENTOR. ffm/ms /VACMY BY @We @mf /fa/M/Y April 6, 1965 1', c, MacAvoY 3,177,082

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BY 'CZ April s, 1965 Filed April 22, 1960 T. C. MaOAVOY ARSENIC SULFIDE GLASSES 3 Sheets-Sheet 3 3,177,082 ARSENlC SULFHDE GLASSES Thomas Ci MacAvoy, Corning, NY., assigner to Corning SlassWorks, Corning, NX., a corporation of New orlr.

Filed Apr. Z2, 1960, Ser. No. 24,103 4 Claims. (Cl. 10d-47) This invention relates to low melting temperature glasses of the arsenic suliide type. It is particularly concerned with a lmethod of modifying certain physical properties of such glasses by means of additives, and with the 'types of thermally sensitive semi-conductor diodes, 'for example, require an encapsulant that is sufficiently iiuid for application, as by coating or dipping, at a temperature not over 350 C. At the same time, the encapsulated unit should become sutliciently rigid for service at temperatures as` high as l50f250 C. This requires a material ihaving a rapidly changing viscosity in this temperature range.l This property is commonly referredto in the glass art as a lvery high viscosity gradient or steepv viscosity curve.r f x l The material should 'also be chemically durable, have a high electrical resistivity and provide other superior velectrical characteristics. Organic polymers possess 'some of these properties, but are generally unsuitable because of 'relatively high vapor permeability and relatively low service temperatures. A primary purpose of the present invention is to provide new glasses that are especially adapted to use as encapsulants.

Attempts have been madeito lower the softening `point and steepen the viscosity curve of vconventional silicate, berate, and phosphate .glasses with additives. These have invariably resulted in glasses that are too hygroscopic ork too water soluble to be satisfactory. Arsenic sulfide glasses have recently been proposed. Such .glasses have proven very useful in many respects. However, their softening points have vnot been as low as desired, nor have their viscosity curves been of the steepness required, for low temperature encapsulation purposes. lt is a specitic purpose of the yinvention to .provide a method of modifying such glasses that corrects the indicated deiiciencies. It has been proposed to modify arsenic sulfide glasses by elemental additives such as Se, Tl, and Te. For the most part lsuch additives have been directed'at modification of infra-red transmitting properties of 'the glass, although thallium is particularly effective also in lowering the softening point of the glass. However, thallium is extremely toxic and difficult to handle in glass production. A more specific purpose of the invention is to provide arsenic sulfide glass additives that are simple and convenient to employ while being effective for other purposes of the invention.

. l `have discovered that halogens and metal halides are miscible with arsenic and sulfur in varying degrees to produce homogeneous glasses characterized by lower softening points and steeper viscosity curves than the parent glass. Iodine is by 'forthe most miscible of the halogens with miscibilit'y decreasingin order from iodine to bromine to chlorine to ilumine. l have also discovered that, of the various miscible metal halides, stannic iodide is by far the most miscible and most eiiective for present purposes.

i aliases Patented Apr. 6, i965 ICC v kmethod or lowering the softening point and steepening the i mental halogens and metallic halides.

viscosity curve of an arsenic sullide glass which comprises incorporating into such glass :a compatible amount of an additive selected from the group consisting of elelt further resides in modilied arsenic sulfide type glasses produced by such method, the preferred additives being elemental iodine or stannic iodide. The term arsenic sulfide glass, means a glass composed basically` of arsenic and sul-fur except as additives are indicated. Limited substitutions of antilmony for arsenic and/ or selenium for sulfur can be made without changing the basic nature of arsenic sulide glasses for present purposes. v

The invention is further described with reference to, and in conjunction with, the accompanying drawings in which,

FIG. l is a ternary or triaxial diagram illustrating and defining a preferred embodiment of the invention, As-S--I glass compositions.

FIG. 2 is a ternary diagram illustrating and dening another embodiment ot the invention, As-SSnl4 glasses and,

FIG. 3 is' a graphical illustration of glass property changes characterizing the invention.

In the ternary diagram of FlG. 1, the apices represent 100% of the indicated elemental component. Any selected point within the axes of the diagram defines, in percent by weighaa mixture of the three elements', arsenic, sulfur and iodine. The curved line A terminates at Zvpoints on the As-S axis, as indica-ted. It defines, with that axis, a compositionparea within which the three indicated component elements are miscible to form glasses.

Each of the substantially vertical dotted lines indicates a series of glass compositions having a common liow temperature, as indicated in C. by the numeral associated with the line. This is a temperature that corresponds approximately to a value of 5 for the log viscosity, in poises, of the glasses.

,It will befobserved that glasses form over an extensive area in the As-S-l system, and that it is possible topincorporate in excess of %V iodine in a properly selected arsenic sulfide base glass As iodine is added to an arsenic suliide base glass, the resulting glasses generally become softer and ultimately are plasticl at room temperature. Compositions intermediate the thermal line designated RT. and line A are of this nature and are subject to tlow under stress at room temperature. These cornpositions become rigid glasses when cooled below room temperature, as in a Dry lee-acetone bath. As-S-I glasses are of a red-amber color, very clear and transparent, and are generally stable against devitritication even upon standing for long periods of time in a plasticcondition.

In melting these glasses, the three components, As, S, and I, are mixed in elemental form, preferably in a state of high purity. The mixture is gradually heated to produce a homogeneous moltenmass. Care should be taken either to provide a non-oxidizing atmosphere, such as argon or nitrogen, or to heat the mixture in a closed or small necked container. This minimizes contact with oxygen which readily reacts with the heated material and/ -or vapors votalized therefrom. As the temperature of the f additive, is incorporated in the glass.

illustration, the logarithm of glass viscosity in poises isv plotted along the vertical axis as a function of glass completion, although additional heat may be supplied if necessary. As indicated, care shouldrbe taken at all stages of the melting process, particularly inV connection,

with stirring, to avoid contact with air or other sources of oxygen. The completely reacted molten mass may either be Cooled in the reaction'chamber, poured into ak mold or other container for cooling, or held in a fluid state for dipping applications. Where the glass is to be applied as a coating or encapsulant, the product beingk treated may be dipped into the molten glass. Alternatively, the glass may be cooled, finely divided, applied tov Vthe article surface and subsequently fused thereto.

In producing glasses as described above, git has been' found that there is a strong tendency for the iodine component -to escape by volatilization. This iodine volatil-izav tion may be suppressedby employing, in lieu of the iodine component, a metal iodide. Monovalent iodides Vsuch as the alkaliiodides, are generallymiscible with arsenic and on glass softening point corresponding to that of iodine. The ternary diagram of FG. 2 generally corresponds to thatrof FIG. lwith the exception thatthe lower right hand apex represents the component stannic iodide rather than `elemental iodine.

glasses. As in FIG. 1, compositionsto the right of and below this line are either immiscible, i.e.- non-glass form-` ing mixtures, 'or devitrifyv upon cooling so that useful glasses are not obtained.

The elements, bromine, chlorine and fluorine cannot conveniently be incorporated in a glass batch in elemental l The line B, terminating on .the As-S axis, deiines the composition Yarea within which the As, S, and Sul, components are Iniscible to Vforml I have found, however, that stannic iodide y is not only the most miscible iodide, but has an effect form for obvious reasons. However, these additives may be introdud inthe form of arsenic bromide, chloride or uoride, respectively. Alternatively, they may be introduced as metal halides, e.g. silver chloride, yantimony fluoride, etc. By way of further illustrating the etfect of 10% I.'r The softening point of thevglass isz indicated by the designation S.P. at about log viscosity of 7.6 on each curve, the softening point of the iodine containing glass being about15 C. lowenthan `that of the base glass.'l The viscosity lcurve'V of they iodine glass, thatis curve D, is markedly steeper atviscosities below the viscosity that defines the glass softening point. curve is more nearly vertical than that of the base` glass shownby curve C. This is indicative of a higher viscosity gradient -or rate of change with temperature `in this significant-region. It will be vunderstood that 'reference to viscosity curves, and to viscosity gradient or curvel characteristics, in this application is in termsl of curves as shown in FIGURE 3, this being ,the familiarmeaning of such terminology in the` glass ant.

While the invention has been described with reference to specific preferred compositions,-it Will'be appreciated c that other halogen and halide modified glasses in accordance with the invention likewise possess such properties in varying degree. Thus, the, glasses arecharacteristically shor-t, or high viscosity gradient, glassesl as illustrated in FIG. 3. They have generally high thermal coeiiicients of expansion, and high electrical resistivities which decrease with increasing amounts of additive;-` They have good durability in water, acids and weak bases, but arek attacked by strong basic solutions, and tend to we othermetals and glasses.

`Of particular interestl for Vencapsulating applications, the glasses are essentially impermeable to vapors. In fact, service testsl indicate that thezforward and yreverse electrical characteristics of semiconductor devices, `such as diodes, encapsulated in the present glasses are actually improved.. vThis suggests that some impurity, such-asv moisture, has been eliminated 'from the .surface Vof the encapsulated device. The exact nature of this change ,is not known, vbutzitseffecthas been con'rmed by repeated tests on semi-conductor devices; that the present glasses are generally clear and transparent bothl in the visible ,red sand in the infra-red regions, the additive apparently not creating any appreciable effect on the infra-red transmission of the basefarsenic sulfide glass. What is claimed is:

1. A method of lowering the wsoftening point and steepening the viscosity curve of an arsenic sulfide glass with` arminimum of volatilizationlossduring melting f 'whichcomprises vincorporating a halide of a polyvalent metal having-an atomic weight greater than l0() into the various additives, the following table sets forth a Variety of different halogen Vand halide additives to an As2S5 base glass, the amount of .additive in the final glass in percent by weight, and the eifect of the additive on the softening point of the glass.

Concen- Additive tration, Result percent Glas, more fluid than AsSs.

o. Glass, softer Vthan AS2S5.

FIG. 3 illustrates the change effected in the kviscosity gradient of an arsenic sulde glass as iodine, the preferred In the graphical temperature inY C. plotted along Ythe horizontal axis.

YCurve C is based onan arsenic sulde glass correspondbatch from which the glass is melted, ,the .metal halide being `incorporated in proportions capable of reacting i with the remaining batch constituents to form a glass,rand thereafter melting the batch to form a *glassV containing the metal halide.

V2. A.method in accordance with claim 1 wherein the.

halide is an iodide.

3.l A method'in accordance with claim 1 'wherein the.

References Cited bythe Examiner y UNITED STATES PATENTS 2,573,380 V10/51 Ambrose et al. 106-47 2,836,544 5/58. Nebergall 1.06,-47 2,883,292 4/59 Jerger 106-47 2,883,294r 4/59' .Terger 1064-47v 2,961,350. -1l/60 Flaschen etal. 106'-47 X 2,979,382 4/61 Frerichs 106-47 TOBIAS iE. LEVOW, Primary Examiner. JOSEPH REBOLD, JOHNR. SPECK, Examiners..

In otherv words, the,

It is 'also' lof interest i 

1. A METHOD OF LOWERING THE SOFTENING POINT AND STEEPENING THE VISCOSITY CURVE OF AN ARSENIC SULFIDE GLASS WITH A MINIMUM OF VOLATILIZATION LOSS DURING MELTING WHICH COMPRISES INCORPORATING A HALIDE OF A POLYVALENT METAL HAVING AN ATOMIC WEIGHT GREATER THAN 100 INTO THE BATCH FROM WHICH THE GLASS IS MELTED, THE METAL HALIDE BEING INCORPORATED IN PROPORTIONS CAPABLE OF REACTING WITH THE REMAINING BATCH CONSTITUENTS TO FORM A GLASS, AND THEREAFTER MELTING THE BATCH TO FORM A GLASS CONTAINING THE METAL HALIDE.
 4. AN ARSENIC SULFIDE TYPE GLASS COMPOSED ESSENTIALLY OF ARSENIC, SULFUR, AND STANNIC IODIDE, EACH OF THESE ESSENTIAL CONSTITUENTS BEING PRESENT IN AN APPRECIABLE AMOUNT ENCOMPASSED WITHIN THE U-SHAPED AREA ON THE TERNARY COMPOSITION DIAGRAM OF THESE COMPONENTS DEFINED BY CURVED LINE B IN FIGURE 2 OF THE DRAWING. 